Characterizing and Modeling the Dynamic Responses, Gas Leakage and Contaminations on the Behavior of the Smart Cement Composite
Cement composites are one of the most durable construction materials, which can be used in different structures. Monitoring the behavior of the cementitious structures is critical during the construction and the entire service life in order to certify the integrity and safety of the structures. This study provides a systematic dynamic characterization of smart cement composites and monitoring gas leakage and contamination in smart oil well cement using electrical measurements. Smart cement composites were developed with up to 75% gravel, 10% hydrophilic polymer resin and few other additives. Investigation of the electrical impedance versus frequency relationship indicated that the smart cement composites can be represented by resistance. Addition of coarse aggregates and hydrophilic polymer resin (HPR) increased the initial electrical resistivity of the smart cement composite as well as long term electrical resistivity. The initial electrical resistivity of smart cement was 1.02 Ω.m which increased nonlinearly to 3.74 Ω.m and 10.55 Ω.m with addition of 75% gravel and 10% HPR respectively. HPR leads to gain zero fluid loss in smart cement composites which is due to polymerized texture of the smart cement composite. The compressible and incompressible fluid flow through porous media has been studied. Vipulanandan fluid flow Model and other models including modified Darcy’ lawwere used to characterize the flow of gas in sand and cement porous media. Experimental results showed that the increasing rate of gas discharge from porous media is not linear with pressure gradient which is due to change in both fluid and porous media properties with pressure. This trend was predicted using the Vipulanandan fluid flow model. Electrical resistivity of the smart cement was measured with nitrogen gas migration under different pressures. The electrical resistivity of the 6 hours cured smart cement decreased by 12% under Nitrogen migration with a pressure of 2 MPa (300 psi). Moreover, the sensitivity of electrical measurements in monitoring the dynamic conditions on smart cement composites such as impact, cyclic loading and cyclic temperature was investigated. Impact loading leads to have up to 2% increment in electrical resistivity for 28 days cured smart cement with resonance frequency of 7.3 Hz. Cyclic loading led to increment in electrical resistivity which is dependable on the displacement rate as well as the ultimate pressure. At a compression stress of 1.03 MPa (150 psi), the change in electrical resistivity is 19.45%, 14.56% and 9.9% respectively for 0.008, 0.016 and 0.032 displacement rates. Temperature changes can change the electrical resistivity of the smart cement. Increasing the temperature from 60° C to 120° C decreased the resistivityby 37% from 12.38 Ω.m to 7.83 Ω.m. Decreasing the temperature from 0° C to -20° C caused an increment of 1692% from 20.19 Ω.m to 361.91 Ω.m. based on experimental studies, a new model has been proposed correlating the rate of change in electrical resistivity, temperature gradient and temperature rate. Finally, contamination and degradation of smart cement with drilling mud or CO2 exposure was studied and the sensitivity of the electrical measurements on monitoring any kinds of contamination on smart cement composites was investigated. OBM Contamination filled up the pores of loose net structure around the cement particles which resulted in increasing in rheological properties of cement slurry. It reduced the development of the resistivity during 28 days of curing due to its hindering effect on the hydration process which caused less production of C-S-H after 28 days. 0.1% and 3% of OBM contamination reduced the resistivity of the cement by 22% and 42% to 9.5 Ω.m and 7 Ω.m respectively. Studies indicated that one of the most significant leakage mechanisms is likely to be flow path of CO2 along cement which can cause cement degradation. CO2 exposure reduced the development of the resistivity during 28 days of curing. 0.1%, 1% and 3% of CO2 concentrated water reduced the resistivity of the cement by 21%, 34% and 38% to 13.4 Ω.m, 11.3 Ω.m and 10.5 Ω.m respectively after 28 days of curing. Vipulanandan p-q model was used to predict the composites’ curing, piezoresistivity behavior, resistivity of the mixtures and pulse velocity variation with curing time.